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A duck, some Newtons, and other fun stuff

  1. Jan 29, 2007 #1
    A duck has a mass of 2.9 kg. As the duck paddles, a force of 0.11 N acts on it in a direction due east. In addition, the current of the water exerts a force of 0.19 N in a direction of 57° south of east. When these forces begin to act, the velocity of the duck is 0.13 m/s in a direction due east. Find the magnitude and direction (relative to due east) of the displacement that the duck undergoes in 2.0 s while the forces are acting.

    What I need are the
    magnitude m
    direction ° south of east

    I've tried drawing free body diagrams, but seem to get stuck. I'm not quite sure how to tell where the duck will be and how to find that in degrees. This is due at 11:30 tonight EST any any guidence would be greatly appreciated!
     
  2. jcsd
  3. Jan 29, 2007 #2

    Doc Al

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    Staff: Mentor

    The first step is to find the net force on the duck. Then apply Newton's 2nd law.
     
  4. Jan 29, 2007 #3
    I've done this thus far:

    Rx = .19(cos 57) +.11(cos0) = .21348N
    Ry = .19(sin 57) + .11 (sin 0) = .1593N
    Ax = .21348/2.9 = .07361 Ay = .1593/2.9 = .0549

    then I do the tan-1 (.0549/.07361) which yields the wrong answer.

    Any suggestions?
     
  5. Jan 29, 2007 #4

    Doc Al

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    Staff: Mentor

    OK. (But realize that the 0.19 N force is south of east.)
    You don't need the angle that the acceleration makes, you need the displacement. Find the change in the velocity in each direction and use it to find the displacement from the initial position. Then worry about finding the angle.
     
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